Method for dissolving cellulose



Patented Aug. 18, 1942 mirnon roa nIssoLvmdcELLULosr: Kurt Hess and Max Ulmann, Berlin, and Richard Weingand, Bomlitz, near many Waist-ode, Ger- No Drawing. Application July 13,1937, Serial No. 153,428. In Germany July 14, 1936 3 Claims. (Cl. 260-215) It has been known for a long time that concentrated sulphuric acid is able to dissolve cellulose fibres into kneadable masses from which cellulose is coagulated in the form of cellulose hydrate by being treatedwith water or with other suitable media, R. Langhans proposes in ,his

German Patent 72,572 for the production of such masses to employ asulphuric acid of 70 to 80 percent after the fibres has been previously treated with a sulphuric acid of 40 to 50 percent. E. Berl uses according to his German Patent 259,248 concentrations of sulphuric acid from 65 to 74 percent for dissolving cotton and wood cellulose.

As well known; when acting upon cellulose by '2 means of suphuric acid of such concentrations, there takes place simultaneously a hydrolytic decomposition of the cellulose which isvery in- .jurious for-,the products to be formed from' the cellulose solutions and hinders the possibility-of manufacturing such products. In order to reduce this detrimental action, R. Langhans dilutes, after the reaction on the cellulose fibres,

the sulphuric acid of 70 to 80 percent by means of a sulphuric acid having'a concentration of .45 to'63 percent. E. Berl avoids the hydrolysis.

According to the invention, it has been found that, when dissolving cellulose in concentrated sulphuric acid, there exists a characteristic small range of concentration of the sulphuric acid within which the cellulose fibres swell up and are clearly dissolved whilst the hydrolytic influences are retarded so strongly that, for obtaining technically useful and valuable products, there is no necessity of executing the solution or the coagulation at a temperature not exceeding 10 centigrade.

As regards natural cellulosefibres this characteristic range of concentration of sulphuric acid extends from 62.5 to 64 percent and, therefore, lies considerably lower than the hitherto prescribed values of concentration. Below this concentration range it is not possible to obtain a solution of the fibres. acid having a concentration lying below this characteristic range, the fibres become substantially only impregnated with sulphuric acid, whilst there is no swelling action and no dis- When using a sulphuric solving effect in the manner required formthe production of homogeneous masses. When-remploying a sulphuric acid having a concentration lying above 64 percent, the hydrolysis becomes already manifest as a disturbing action so that the use of this concentration requires the. observing of the known precautions necessary-for obtaining useful masses. When working within the indicated. range of concentrations, thereis the particular advantage consisting in that the temperature can' be reduced to 0 centigradeat the beginning of the reaction. Owing to the'small concentration of the sulphuric acid thesolutions remain stable for a long time at thi's'temperature without provoking the injurious hydrolysis. This is of great importance because, in this way, sufficient time is available for the further treatmnt of the masses, without influencing linjuriously thereby the quality of the obtainedlprod- After having kneaded the mass at llfjcenti grade.

it is advantageous to cool down thestill several hours to temperatures below 0 centi grade, for instance, to about 5'to -'l centigrade in order to perfect the solution before the coagulation. When working in this manner,

there is thevspecial advantageconsisting in that the coagulation,can be obtained without further ado at normal or room temperature. A characteristic feature of the .method according tothe,

invention consists also in that the use of the sulphuric acid having the specified low concentrations allows to avoid carrying out the solution at temperatures of below 10 centigrade which are prescribed as indispensablein the German Patent 259,248 of Berl. At this temperature, the fibres remain undissolved under. the conditions of the method of the invention even during several days.

As initial materials for the method according to the invention are useful bleached cotton linters as well as the bleached sulphate or soda cellulose prepared from wood. It is even possible to work with the cellulose in the form of board if they are pressed as little as possible on the paper manufacturingmachine so as to retain a loose structure and, thereby, to possess an advantageous capacity of absorbing the acid. As particularly useful has been proven a soda or sulphate cellulose decomposed by means of the sodium or sulphate process and which is improved by means of a subsequent alkaline tretament to such a degree that it shows a content of alpha cellulose exceeding percent and being preferably of 96 percent When transforming this tained qualities.

cellulose into the form of board, this process is executed so as toobtain a board or a structure as loose as possible. i

To sum up, according to the invention, when producing plastic masses, toils, filaments and other products from celluloseby means of sulphuric acid, the following advantages are obproposed for manufacturing these products by the use of sulphuric acid:

1. A considerable economy as regards sulphuric acid, v 2. A much simpler technical execution of the process owing to the omission of the excessive cooling to temperatures not exceeding -10 centigrade, t

'3. Stability and durability of the solutions during relatively long periods of time which is important for the subsequent technical treatment, a I

4. Owing to the use of sulphuric acid having low concentrations, the coagulation can be made to take place at normal or room temperature instead at temperatures not exceeding -10 centigrade, I

5. The possibility of employing wood cellulose.

From the solutions prepared according to the invention it is possible to manufacture all the products as produced today from viscose or from ammoniacal copper oxide cellulose, for instance,

' filaments, toils, bands, seamless tubes, sponges and other products with valuable technical Example 1 1 part of soda cellulose having a good absorbing capacity and being in the form of a board with'an alpha-cellulose content of 96 percent is mixed with 9 parts of sulphuric acid of 63.3 percent cooled to centigrade. The mixture is thoroughly kneaded in a kneading machine and in comparison with the processes hithertor with 8 parts of sulphuric acid or 62.8 percent as is left at rest during several hours. Then the mass is cooled down to about 7 centigrade during kneading until it is perfectly clear and capable of being spun into threads. The coagulation is carried out by pouring out the solution in the form of a thin layer and by introducing it into water at room temperature for the purpose of producing a foil.

Example 2 1 part of cotton linters is mixedand treated described in connection with Example 1.

Of course the invention may be carried out in detail also in a manner difiering from the above examples, for instance, by choosing other proportions of the cellulose and the acid.

Having now described and ascertained the nature of our invention we declare what we claim is:

l. A process for dissolving cellulose comprising initially treating cellulose with a sulphuric acid solution of a concentration of from 62.5% to 64% at a temperature of approximately 0 C. for a period of several hours.

2. A process for dissolving cellulose comprising initially treating cellulose. with a sulphuric acid v solution of a concentration of from 62.5% to 64% at a temperature of 0 to --7 C. for a period of several hours.

3. A process for dissolving cellulose comprising initially treating cellulose with a sulphuric acid solution of a concentration of from 62.5% to 64% at a temperature of approximately 0 C. for a period of several hours and thereafter reducin the temperature of the solution to approximately KURT HESS- 7 MAX ULMANN. RICHARD WEINGAND., 

